Technical Abstract:
Skatole is a potent odorant produced by anaerobic degradation of stored animal waste materials. Little is known of the phylogeny of skatole-producing microorganisms or the conditions that favor their growth. These deficiencies hamper attempts to reduce skatole production. Previous studies suggest that acetogens may be important in the conversion of indole-3-acetic acid (IAA) to skatole. The goal of this study was to enrich for homoacetogenic microorganisms present in swine lagoon slurry (SLS) which are also capable of skatole production. To this end, SLS (100 µl) was added to anaerobically incubated acetogen media containing no added carbon source except 100 µM IAA. GC-MS was used to measure skatole production in the acetogen enrichments after 0, 7, 21, 28 and 42 days incubation. The enrichments were tested for an increase in total cell concentration using quantitative, real-time PCR of the 16S rDNA gene and the presence of acetogens was evaluated by PCR amplification using primers specific to the formyltetrahydrofolate synthetase (FTHFS) gene (a highly conserved gene important in a key step in the formation of acetate). Results show that skatole production increased from 0 ng mL-1 on day 0 to a high of 4.7 ng mL-1 on day 28 before decreasing to below detectable levels on day 42. Skatole concentrations in sterile and non-sterile controls with no IAA added never increased above the limit of detection. Total cell concentrations increased from 1.30 ' 0.50 X 105 cells mL-1 following inoculation on day 0 to 1.41 ' 0.25 X 107 cells mL-1 by day 42. FTHFS analysis of day 42 samples show that acetogens were present in IAA supplemented samples, but were absent in sterile and non-sterile control samples. PCR products (16S rDNA and FTHFS) from these enrichment samples are currently being sequenced to provide phylogenetic data about the identity of organisms in these samples. These data suggest that acetogens may be associated with skatole production.